Fuel injection pump for internal combustion engines

ABSTRACT

What follows is a description of an improved fuel injection pump for an internal combustion engine. The pump includes a rotating and reciprocating piston which distributes fuel through a fuel passage provided in the pump for each fuel injection nozzle of the pump. To avoid the adverse effects which result from the reduced fuel pressure during the suction stroke of the pump, an improved pressure relief apparatus is provided. The improvement resides in two coaxially disposed blind bores in the piston and associated radial bores extending radially from the blind ends thereof. The coaxially disposed blind bore and its associated radial bore closest to the working chamber of the pump serve as a passage for supplying fuel to be distributed and as a passage through which fuel is distributed, while the coaxially disposed bore farthest from the working chamber of the pump includes a spring-loaded valve which opens in the pressure relief direction.

' States Patent 11 1 1451 Nov. 19, 1974 FUEL INJECTION PUMP FOR INTERNAL COMBUSTION ENGINES Primary Examiner-Charles .1. Myhre Assistant Examiner-Tny Argenbright [75] Inventor. Gerald Hofer, Flacht, Germany Attorney, Agent or Firm Edwin E gg [73] Assignee: Robert Bosch GmbH, Stuttgart,

Germany [22] Filed: Nov. 1, 1973 [57] ABSTRACT [21] Appl' 411824 What follows is a description of an improved fuel injection pump for an internal combustion engine. The [30] Foreign Ap lication Priorit Data pump includes a rotating and reciprocating piston P 1 Nov. 29, 1972 Germany 2258309 which distributes fuel through a fuel Passage Provided in the pump for each fuel injection nozzle of the 52 CUB/139 B1), 123/139 AD, 123/139 AF, pump. To avoid the adverse effects which result from 123/139 AL 123/139 R the reduced fuel pressure during the suction stroke of 51 1111. C1. F02m 41/08 the Pump, an improved Pressure relief apparatus is Field f s 123/139 R, 139 AD, 139 AF provided. The improvement resides in two coaxially 23 9 ED 13 AL, 40 B disposed blind bores in the piston and associated radial bores extending radially from the blind ends 5 References Cited thereof. The coaxially disposed blind bore and its as UNITED STATES PATENTS sociated radial bore closest to the working chamber of 2 640 419 6 1953 E I 123 139 BD the pump serve as a passage for supplying fuel to be 2'765'741 141956 R X d1str1buted and as a passage through which fuel 1s d1s- 2'775'233 12/l956 23221}; 124N391: tributed, while the coaxially disposed bore farthest 2 794397 6/1957 Burman. 123 139 BD from the Working chamber of the Pump includes a 2:965:087 12/1960 Bischoff a a1. 123 139 BD Spring-loaded valve which Opens in the Pressure relief 3,023,705 3/1962 Heiser 123 139 BD x direction- 3,058,455 10/1962 Hofer et al. 123/139 BD FOREIGN PATENTS OR APPLICATIONS 6 Claims 2 Drawing Figures 69,587 11/1958 France 123/139 BD FUEL INJECTION PUMP IFOR INTERNAL COMBUSTION ENGINES BACKGROUND OF THE INVENTION The present invention relates to a fuel injection pump for internal combustion engines of the type having a simultaneously rotating and reciprocating pump piston actuated and controlled by a cam. The fuel pump under consideration serves as a fuel distributor which distributes fuel through alternating ones of the supply channels disposed within the circumference of a cylinder of the pump, the number of supply channels corresponding to the number of the engine cylinders to be supplied. The pump has a pressure relief apparatus which is operative in dependence on the rpm of the engine during the piston supply stroke and after interruption of the fuel supply to effect control of the fuel pressure in the supply channels and conduits leading to the fuel injection nozzles of the pump.

In a known fuel injection pump, a control of the fuel quantity occurs by means of an adjustable throttle in the suction channel leading to the pump work chamber. In these pumps, during partially loaded operation, a sharply reduced (negative) pressure occurs, during the suction stroke, in the pump work chamber and in the channels connected thereto. This leads to vapor bubble formation, unequal injection and cavitation damage. In order to avoid these disadvantages, each injection line of the fuel injection pump contains a relief valve with a relief piston, and furthermore the connecting channel between this relief valve and the control point of the injection line is separated from the pump work chamber during the suction stroke and is relieved by a connecting line leading to the pump suction chamber. For this purpose, however, two further control points, a separate entry channel and an expensive relief valve for each injection line are required which results in considerable expense.

OBJECT AND SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to overcome the deficiencies noted above in an injection pump of the type described by simple means and at considerably less expense; and by a suitable disposition of elements to avoid the formation of a reduced pressure condition with the consequent cavitational damage and unequal injection of fuel quantities that occur even during engine modes requiring high supply rates or at higher pressures.

This as well as other objects are achieved according to the present invention by providing a pump wherein the pressure relief apparatus comprises two coaxially disposed blind bores and a radial bore for each of the two coaxially disposed blind bores formed within the pump piston. The coaxially disposed blind bore and its associated radial bore closest to the working chamber of the pump serve as a passage through which fuel is distributed, while the coaxially disposed bore farthest from the working chamber of the pump includes a spring-loaded valve which opens in the pressure relief direction.

The improved pump according to the present invention has an advantage that during the suction stroke of the pump piston a reduced pressure can occur only in the region of the upper relief channel portion that is connected with the pump work chamber. The pressure fluctuations occurring in the supply channel and in the injection lines connected thereto can be made to decay through the single central relief valve, and furthermore, the median pressure can be held constant there. Beyond this, even after the relief valve has opened and during the fuel supply or power stroke, a constant pressure can be maintained in the pump volume and in its connection to the central relief valve.

An advantageous embodiment of the present invention consists in that the distribution bore at the third control point can be closed shortly after the beginning of the suction stroke of the pump piston and earlier than the radial bore of the lower part of the relief channel at the second control point can be closed and in that both are operable at the same time. Both the second and third control points are defined below.

This has the advantage that after closing the distribution bore, the supply channel can be further pressurerelieved during the beginning of the suction stroke of the pump piston, and that when the distribution bore is open, a certain amount of fuel can stream backwards into the pump working chamber after the top dead center position of the pump piston and during an exactly determinable portion of the beginning suction stroke. This corresponds to a supplementary volumetric relief of the supply channel of the injection line.

Another advantageous embodiment of the present invention consists in that the driving cam for the pump piston has a flat portion at the top dead center. This also provides an advantageous possibility of achieving a further relief and pressure equalization in the supply channels prior to the beginning of the suction stroke when using the device according to the present invention. The disposition described above achieves in an advantageous manner that no reduced pressure occurs and therefore cavitation damage and unequal injection are avoided, even during higher supply performance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a longtudinal cross section of the fuel injection pump according to the present invention.

FIG. 2 is a timing diagram showing the opening times of the individual control points which are shown with respect to the stroke development of the pump piston.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now more specifically to FIG. 1 there is shown a pump having a housing 1 within which a cylinder 4 formed by a sleeve 3 is firmly mounted. A piston 2 reciprocates within the cylinder 4. The piston 2, which is embodied as a fuel distributor, sequentially supplies several cylinders of an internal combustion engine. For this purpose, the piston 2 is mounted for simultaneous rotary and reciprocating motion according to the arrow shown in FIG. 1. The rotary and reciprocating motion is achieved by a driven cam 6 which runs on rollers 7 which in turn are pressed against the cam 6 by means of a spring (not shown). The transmission of rotary motion between the cam disc 6 and the piston 2 occurs by means of a pin 8 which engages a groove 9 at the bottom 10 of the piston 2.

During each suction stroke of the piston 2, fuel is supplied from a suction chamber 16 to a working chamber 12 enclosed within the pump piston 2 and the cylinder 4 after passing through a supply channel 13, a supply bore 14 and one of the longitudinal grooves 15. The suction chamber 16 is supplied with fuel by a delivery pump 34 drawing fuel from the tank 35. The pressure in the suction chamber 16 is controlled in an rpm-dependent, known manner by means of a pressure control valve 36.

Along the longitudinal axis of the piston 2 there is formed a relief channel consisting of an upper portion 17 which includes a blind bore. The channel 17 starts at the working chamber 12 and extends to a radial bore 22. A lower relief channel portion 18 also in the form of a blind bore is provided. The channel portion includes an upper portion 20 and a lower portion 19. The bottom portion of the piston 2 has a larger diameter than the terminal portion 10. The radial bore 22 serves as a distribution bore, opening into the lower end of the relief channel portion 17 within the terminal portion 10'. Another radial bore 23 opens into the upper portion of the lower relief channel 18. A transverse bore 24 terminates in the lower portion 19 of the lower relief channel 18. The exit of this lateral bore 24 cooperates with a control sleeve 26 which can be axially displaced on the pump piston 2 in accordance with the load and the rpm of the engine.

For that purpose there is provided a lever 37 which is pivotable about a pin 38 fixed in the housing 1. The lever 37 carries a spherical head 39 which engages a complemental recess 40 provided in the control sleeve 26. On the other end the lever 37 may be connected to a centrifugal governor and a regulator spring such as described e. g. in U.S. Pat. No. 3,635,603.

The relief channel portion 18 is closed from the bottom end of the piston 2 by a screwed-in stud 27. By means of the stud 27 and in dependence on the depth to which it is inserted, a spring 28 can be adjustably pretensioned. Of course, a suitable bolt can also be pressed in. The spring 28 presses against a ball 30 which in turn presses against the seat formed between the portions 19 and 20 of the relief channel part 18 whereby the transition from the portion 19 to the portion 20 is sealed tightly.

The distribution bore 22 and the radial bore 23 can be connected with one another by means of a U-shaped connecting channel 32, which is formed in the sleeve 3.

Beginning at connecting channel 32, there branches off one of a plurality of fuel supply lines 33 which leads to the injection nozzles (not shown). These supply channels 33 and the connecting channels 32 are disposed around the circumference of the pump piston 2 depending on the number and the sequence of the cylinders of the internal combustion engine which are to be supplied.

For convenience the following definitions are noted: a first control point (I) is defined by the control sleeve 26 and the lateral bore 24; a second control point (II) is defined by the radial bore 23 and the connecting channel 32; and a third control point (Ill) is defined by the radial bore 22 and the connecting channel 32.

The mode of operation of the fuel injection pump according to the present invention is as follows:

The cam plate 6 is driven and rotates over the rollers 7. This in turn causes the pump piston 2 to execute, as has already been described, a rotating and reciprocating motion, where during its downward motion or suction stroke, it aspirates fuel from the suction chamber 16 through the supply channel 13, the supply bore 14 and one of the longitudinal grooves 15 disposed at the upper circumference of the pump piston 2 and delivers it to the working chamber 12. During this process, the connections between the distribution bore 22, the radial bore 23 and the connecting channel 32 are closed, but then the piston is rotated for the connections to be opened during the power stroke. During the power or supply stroke of the piston 2, the fuel flows from the working chamber 12 through the upper relief channel portion 17, the distribution bore 22, the connecting channel 32, and the supply channel 33 to the fuel injection nozzles (not shown). In addition the open connections permit fuel to flow through the relief valve 30 into the lower relief channel portion 18. In the first instance, that is during a first phase of the power stroke, the first control point, comprising the control sleeve 26 and the lateral bore 24, is closed so that the fuel is delivered exclusively to the nozzles. Depending on the position of the control sleeve 26, the first control point is eventually opened prior to the pistons reaching its top dead center, so that the fuel drains through the relief valve 30, the lateral bore 24 and into the suction chamber 16. When the top dead center position is reached, the connection between the distribution bore 22 and the connecting channel 32 which together form the third control point, is closed by rotation of the piston 2.

These events and the opening times of the remaining control points can be seen in the schematic timing diagram of FIG. 2 which shows the stroke of the piston 2 as a function of its rotation. The designation Ill represents the duration of the connection of the distribution bore 22 with the connecting channel 32 at the third control point. In contrast to the third control point the second control point, designated by the reference ll and comprising the radial bore 23 and the connecting channel 32, remains open longer, for the same onset, than does the third control point and it remains open for nearly the entire suction stroke. The closing of the third control point to begin the suction stroke assures that the motion of the piston 2 does not produce a reduced pressure in the connecting channel 32, the supply channel 33, or the second relief channel portion 18. After the third control point is closed, i.e., at the end of the power or supply stroke, pressure pulses which are created in the injection lines can decay through the relief valve 30. What is especially achieved, depending on the spring pressure in the relief valve 30, is that a uniform relief pressure is achieved in the supply channels and in the injection lines. In addition, the central valve maintains a constant pressure in the pump chamber and the adjacent bores an instant after the lateral bore 24 is opened by the control sleeve 26. By changing the pretension of the spring 28, the pressure which is to be maintained in the supply lines after closing the nozzles, can be determined. With this disposition, reduced pressures which are caused by the suction process and which lead to unequal injections as well as reduced pressures which occur through pressure fluctuations in the supply channels and injection lines, and which lead to cavitation damage and to irregular injection, are avoided.

The extension of the opening time at the third control point beyond the top dead center of the pump piston 2 at the beginning of the suction stroke makes possible that a predetermined amount of fuel can be withdrawn for thesupple'mentary volumetric relief of the supply channels. In another embodiment, the cam which controls the motion of the pump piston 2 can have a short flat portion R at the top dead center, during which the piston stands still, by which means a pressure equalization and a decay of the pressure fluctuations in the supply system is also achieved.

What is claimed is:

1. In a fuel injection pump for internal combustion engines, including: (a) a housing; (b) a cylinder mounted within said housing and having a central bore and a plurality of fuel supplying bores formed about the circumference of said cylinder and extending substantially radially from said central bore; (c) a plurality of channel means within said housing, each extending between a fuel injection nozzle and a fuel supplying bore, said channel means and their operatively associated fuel supplying bores forming a plurality of fuel paths, one for each of the fuel injection nozzles, said plurality of fuel paths being equal in number to the number of engine cylinders supplied by said pump; (d) a piston,

said cylinder and said piston defining a work chamber; (e) cam means for rotating and reciprocating said piston within said central bore; said piston serving, as a result of its motion within said central bore, to distribute fuel through respective ones of said plurality of fuel paths; (f) relief channel means defining a first control point; (g) relief valve means operatively associated with said relief channel means, said relief valve means being adapted to open during the fuel supply stroke of said piston, as a function of engine rpm and after the fuel supply to said fuel paths has been interrupted to thereby control the fuel pressure of the fuel quantity within said fuel paths, the improvement wherein:

A. said relief channel means comprises two coaxially disposed blind bores within said piston and two radial bores one for each of said coaxially disposed blind bores, each said radial bore extending radially from the blind end of its respective blind bore;

B. two fuel supplying bores are provided for each associated channel means with each of said radial bores being operatively associated with a respective one of each of said two fuel supplying bores,

and with one of said radial bores and its operatively associated fuel supplying bores defining a second control point and the other of said radial bores and its operatively associated fuel supplying bores defining a third control point;

C. said coaxially disposed blind bore closest to said work chamber and said third control point serving as a passage for supplying fuel to be distributed and as a passage through which fuel is distributed; and

D. said coaxially disposed blind bore farthest from said work chamber and which extends between said first control point and said second control point including a spring-loaded valve which opens in the pressure relief direction.

2. The fuel injection pump as defined in claim 1, wherein the radial bore of said third control point is closed shortly after the beginning of the suction stroke of said piston and before the radial bore of said second control point, and wherein both said radial bores are opened together.

3. The fuel injection pump as defined in claim 1, wherein said cam means includes a flat portion which is effective when said piston reaches its top dead center.

4. The fuel injection pump as defined in claim 1, wherein the first control point is defined by a control sleeve mounted to be axially slidable on said piston as a function of engine load and rpm, and a transverse bore formed in said piston and extending from the coaxially disposed blind bore farthest from said working chamber, said control sleeve controlling as a result of its sliding movement the opening and closing of said transverse bore.

5. The fuel injection pump as defined in claim 1, wherein the radial bore of said second control point communicates with its corresponding fuel supplying bore during the supply stroke of said piston and during a major portion of the suction stroke of said piston.

6. The fuel injection pump as defined in claim 1, wherein means are provided for varying the pretension of said spring-loaded valve. 

1. In a fuel injection pump for internal combustion engines, including: (a) a housing; (b) a cylinder mounted within said housing and having a central bore and a plurality of fuel supplying bores formed about the circumference of said cylinder and extending substantially radially from said central bore; (c) a plurality of channel means within said housing, each extending between a fueL injection nozzle and a fuel supplying bore, said channel means and their operatively associated fuel supplying bores forming a plurality of fuel paths, one for each of the fuel injection nozzles, said plurality of fuel paths being equal in number to the number of engine cylinders supplied by said pump; (d) a piston, said cylinder and said piston defining a work chamber; (e) cam means for rotating and reciprocating said piston within said central bore; said piston serving, as a result of its motion within said central bore, to distribute fuel through respective ones of said plurality of fuel paths; (f) relief channel means defining a first control point; (g) relief valve means operatively associated with said relief channel means, said relief valve means being adapted to open during the fuel supply stroke of said piston, as a function of engine rpm and after the fuel supply to said fuel paths has been interrupted to thereby control the fuel pressure of the fuel quantity within said fuel paths, the improvement wherein: A. said relief channel means comprises two coaxially disposed blind bores within said piston and two radial bores one for each of said coaxially disposed blind bores, each said radial bore extending radially from the blind end of its respective blind bore; B. two fuel supplying bores are provided for each associated channel means with each of said radial bores being operatively associated with a respective one of each of said two fuel supplying bores, and with one of said radial bores and its operatively associated fuel supplying bores defining a second control point and the other of said radial bores and its operatively associated fuel supplying bores defining a third control point; C. said coaxially disposed blind bore closest to said work chamber and said third control point serving as a passage for supplying fuel to be distributed and as a passage through which fuel is distributed; and D. said coaxially disposed blind bore farthest from said work chamber and which extends between said first control point and said second control point including a spring-loaded valve which opens in the pressure relief direction.
 2. The fuel injection pump as defined in claim 1, wherein the radial bore of said third control point is closed shortly after the beginning of the suction stroke of said piston and before the radial bore of said second control point, and wherein both said radial bores are opened together.
 3. The fuel injection pump as defined in claim 1, wherein said cam means includes a flat portion which is effective when said piston reaches its top dead center.
 4. The fuel injection pump as defined in claim 1, wherein the first control point is defined by a control sleeve mounted to be axially slidable on said piston as a function of engine load and rpm, and a transverse bore formed in said piston and extending from the coaxially disposed blind bore farthest from said working chamber, said control sleeve controlling as a result of its sliding movement the opening and closing of said transverse bore.
 5. The fuel injection pump as defined in claim 1, wherein the radial bore of said second control point communicates with its corresponding fuel supplying bore during the supply stroke of said piston and during a major portion of the suction stroke of said piston.
 6. The fuel injection pump as defined in claim 1, wherein means are provided for varying the pretension of said spring-loaded valve. 